crypto: chtls - remove the redundant check in chtls_recvmsg()

A warning message reported by a static analysis tool:
  "
  Either the condition 'if(skb)' is redundant or there is possible null
  pointer dereference: skb.
  "

Remove the unused redundant check.

Signed-off-by: Yunfeng Ye <yeyunfeng@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>